Short and long-term outcomes of outborn vs. inborn infants <32 weeks’ in Western Australia: A cohort study of infants born between 2005 and 2018

Objective To compare mortality and morbidity of inborn vs outborn very preterm infants <32 weeks’ in Western Australia between 2005 and 2018. Design Retrospective cohort study Patients Infants <32 weeks’ born in Western Australia Main outcome measures Mortality was assessed as death before discharge home from the tertiary NICU. Clinically significant short-term morbidities included combined brain injury (intracranial haemorrhage (ICH) Grade ≥ 3 and cystic periventricular leukomalacia (cPVL)) and other important major neonatal outcomes. Standardised developmental assessments up to 5 years of age were evaluated where available. We performed multivariable logistic regression analysis of outborn status on outcomes, controlling for gestational age, birthweight z-score, sex and multiple birth Results A total of 4974 infants were born in WA between 22 - 32 weeks’ gestation between 2005 – 2018 of which 4237 (89.6%) inborn and 443 (10.4%) outborn were compared. Overall mortality to discharge was higher in outborn infants (20.5% (91/443) vs. 7.4% (314/4237); aOR 2.44, 95% CI 1.60-3.70, p<0.001). Outborn infants had higher rates of combined brain injury than those inborn (10.7% (41/384) vs. 6.0% (246/4115); adjusted OR 1.98, 95% CI 1.37 – 2.86), p<0.001). No difference in long-term neurodevelopmental measures was detected, however, long-term follow-up data were available for only 65% of outborn and 79% of inborn infants. Conclusions Outborn preterm infants <32 weeks in WA have increased odds of mortality, and combined brain injury than those inborn. Long-term outcome results is likely to be affected by incomplete follow-up data.